Radio wave trap



Nov. 19, 1929. 1J. MGDONALD 1,736,614

RADIO WAVE TRAP n Filed June 9, 1.927

tofm up Patented Nov. 19, 1929 UNITED STATES PATENT OFFICE JAMES J.MCDONALI), OF SANk JOSE, CALIFORNIA RADIO WAVE TRAP applicativa filedJune 9, 1927. serial ivo.' 197,734.

capable of being connected with said first and second inductances ininductive relation therewith, whereby undesirable signals or wavesemitted from any transmitting station may be successfully trapped, anddesired signals received without overlapping interference from othersignals.

An object of the invention is to provide an improved type of wave trapin which a plurality of inductances are inductively related andcontrolled by a single variable condenser for more efficiently trappingor cutting out radio signals from overlapping waves emitted from atransmitting station, or for trapping the waves from a nearby station,when it is desired to receive the Waves from a more distant station,which are rendered inaudible or indistinct, due to the high power of thenearby station.

A further object of the invention is to provide a wave trap of the typementioned, to-

gether with means for selectively connecting the trap in the antennacircuit of a radio receiving set, or for disconnecting the sametherefrom.

Other objects will appear as the description proceeds. In theaccompanying drawings which form a part of my application The singlegure is a diagrammatic showing of my improved wave trap showing the sameconnected in the antenna circuit of a radio receiving circuit.

Like characters of reference are used throughout the followingspecification and the accompanying drawings to designate correspondingparts.

A primary inductance l is formed by winding the desired number of turnsabout a form in spaced relation, the said windings being electricallyconnected through the wire 2 and grouped at the oppositeends of theform. A second inductance 3 is Awound upon a suitable form adjacent thefirst mentioned form and consists of two electrically connected andshort circuited spaced groups of windings, inductively7 connected withthe windings or inductance l. l third winding 4 is woundl upona suitableform, preferably at right angles to the winding 3 and within theinductivev field of the same, and also consists lof two electricallyconnected spaced groups of windings which are short circuited, andvisadapted to vbe selectively connected with the 'inductance winding l,vthrough themedium ofthe switch 5 and conductor 6.

An antenna 7, variable condenser 8 preferably of twenty-three platetype, and single pole, singlefthrow switch 9, are connected with theinductances 1, 3 and 4, and comprise the'essential parts ofthe wavetrap. j

v4The wiring diagram or hook-up illustrated in the singleffigure is asfollows The antenna? is connected to one end of the induc-y tancewinding yl, while the other end ofthe said vwinding is connected to theradio receiving set. The variable condenser l3 is shunted across'thevinductance winding l. Theends ofthe inductance winding 3 are shortcircuited-and are connected to the wire connecting the variablecondenser and the receiving set. The winding 3 is also electricallyconnected with ythe inductance winding 1'. Hence, it will be'seen thatthe short circuited inductance Winding 3 is inductively positioned withrespect to the inductance winding l. Likewise the third inductancewinding 4 is short circuited and may be electrically and inductivelyconnected with the windings 1 and 3 when desired, by merely closing theswitch 5. 4 are placed in the magnetic eld of coil 1, a decidedinductive effect will be set up in coil 4. The coil 4 being connected tothe rotor side of the condenser gives the coil 4 a variable inductance.

The method of operating the wave trap is similar to the method ofoperating a wave trap utilizing a single inductance winding and variablecondenser shunted across it, in the antenna circuit. However, it will beSince the coils 3 and found that when the trap is in the antennacircuit, a very small change in dial setting will be required. Theinductive efect between the inductance windings l, 3 and 4, 5 due to theclosed or short circuited winding of the inductances 3 and 4: will causea consequent increase in the efficiency of the trap. The desired waveswill pass through the fcoi or inductance winding 1, while the windings 3and 4 connected with one ,side .of the variable condenser acts to trapthe undesired or interfering waves or signals.

It is pointed out that the importance and efficiency of this type ofwave tmp depends on the manner in which the windings 3 and 4 areconnected. The action fof the windings 3 .and 4 is entirely inductive:1a-s negar-ds the winding i. The third winding-may Jole-scounected withthe windings l land 3, when it is zo desired to trap interfering 'waivesfrom extremely high power .stations in -c'lose pmximity to the receivingset.

From the iEor-egoing description, it will 'he understood that I do `notintend to limit my self to the :specificccnstmtctionrdeecribed, but

rather .by the terms of the appended I.c1aim:-

1. A wave trap rer rad-io circuits including an antenna connection, aprimary Wind 3g ing in series therewith, a Variable condenser shuntedacross saidprimary winding, a short circuited winding inductwely.connected with said primary winzding@` and 1a, second short circuitedWin-ding selectively connected in nductive relation vwith said irstvrrientirmedshort circuited winding. Y Y

2. A wave trap for radio circuits .including ian antenna commotion, aprimary winding in series therewith, a vari-ablecondenser o shuntedacross said primary winding, a vshort circuited s lit windinginductively .connected with said primary winding, .and a 'second shortcircuited .split Winding selectivel connected in inductive relation with`first mentioned short .circuited split winding,

In testimony whereof I have hereunto affixed `my signature, Y

JAMES J. MCDONALD.

